Retroreflective articles have the ability to return a substantial portion of incident light in the direction from which the light originated. This unique ability has lead to the widespread use of retroreflective articles on clothing worn by highway construction and maintenance workers and fire-fighters. The retroreflective articles displayed on their clothing typically are in the form of retroreflective stripes on a fluorescent background. The retroreflective articles improve the wearers' safety by highlighting their presence. This is accomplished by providing enhanced conspicuity to the garment under both daytime and nighttime lighting conditions. In daytime lighting conditions (strong diffuse ambient light), the fluorescent portion of the article provides the enhanced conspicuity by absorbing non-visible light and retransmitting that light in the visible spectrum. In nighttime lighting conditions (low diffuse ambient light), the retroreflective stripes provide the enhanced conspicuity by becoming illuminated when light from motor vehicle headlamps and search lights strikes the retroreflective articles.
The retroreflective, fluorescent-colored articles have been made by coating a layer of fluorescent material comprising a fluorescent pigment in an organic binder onto a fabric substrate, and then laminating or otherwise bonding a retroreflective material of the desired configuration to selected areas of the surface of the fluorescent-colored fabric. In many cases, the back surface of the fabric substrate (opposite the fluorescent surface having the retroreflective materials attached thereto) is then sewn, laminated or otherwise attached to selected areas of the garment that is worn by the highway worker or fire fighter. An example of this type of product is disclosed in U.S. Pat. No. 4,533,592 to Bingham. A detailed cross-section of a prior art retroreflective article that can be secured to the outer surfaces of a garment is shown in detail in FIG. 1.
Retroreflective article 10 illustrated in FIG. 1 includes a retroreflective segment 12 bounded by two colored segments 14 and 14'. Retroreflective segment 12 includes a multitude of optical elements, typically microspheres 18 partially embedded in a binder layer 20. A specularly-reflective metal layer 22 is disposed behind the embedded portions of the microspheres 18. Retroreflective segment 12 may extend over the surface of a colored fabric 15 as a stripe. Colored fabric 15 typically includes a fluorescent-colored coating 24 on a fabric 26. When viewed from location X under strong diffuse ambient light, product 10 is seen as a grayish stripe (segment 12) bounded on both sides by a fluorescent-colored fabric noted as colored segments 14 and 14'. Under nighttime viewing conditions, the retroreflective stripe essentially is the only portion of article 10 that is highly visible when light is shined thereon.
Although product 10 can provide excellent conspicuity by highlighting a wearer's presence under both strong and low ambient lighting conditions, the retroreflective product has four major drawbacks: (i) excess layers of material are used in the construction 10; (ii) the retroreflective segment 12 can become delaminated from the underlying colored fabric 15; (iii) solvent-based binders and adhesives are frequently employed in the manufacture of the retroreflective segments 12 and in their application to the colored substrate 15; and (iv) there is essentially no retroreflectivity in the colored segments 14, 14' of the articles. Delamination of the retroreflective segment 12 from article 10 causes the garment to lose its nighttime conspicuity. Excessive layers of material make the garments heavier and less flexible and can increase product cost. Use of solvent-based binders and adhesives is unfavorable because they often require expensive solvent-recovery equipment to avoid polluting the environment.
To provide retroreflective articles with portions having varying degrees of retroreflectivity to display an image or some kind of pattern on the front side of the retroreflective article, a vapor-coated, specularly-reflective metal layer has been placed behind the optical elements of the sheeting in selected areas. The selective placement of the vapor-coated, metal reflective layers has been accomplished in a few different ways. A commonly-used method involves vapor-coating a continuous, specularly-reflective metal over the whole back surface of the optical elements, placing a protective layer over the portions of vapor-coated metal, and using an etchant solution to remove the unprotected areas of metal. A method of this kind is disclosed in U.S. Pat. Nos. 5,264,063, 4,801,193, and U.S. patent application Ser. No. 08/181,619 filed Jan. 13, 1994. U.S. Pat. No. 4,645,301 discloses a distinctly different method of selectively placing a specularly reflective metal behind optical elements. The method disclosed in this patent involves use of a laser and selective chemical removal of a continuous vapor-deposited metal layer. Although the above methods can selectively place a vapor-coated, specularly-reflective metal behind the optical elements of a retroreflective sheeting, these methods are relatively complicated and involve use of a solvent that must be disposed of in an environmentally sound manner.